Solid state lighting (SSL) is rapidly becoming the norm in many lighting applications. This is because SSL elements such as light emitting diodes (LEDs) can exhibit superior lifetime and energy consumption, as well as enabling controllable light output color, intensity, beam spread and/or lighting direction.
Tubular lighting devices are widely used in commercial lighting applications, such as for office lighting, for retail environments, in corridors, in hotels, etc. A conventional tubular light fitting has a socket connector at each end for making mechanical and electrical connection to connection pins at each end of a tubular light. Conventional tubular lights are in the form of fluorescent light tubes. There is a huge installed base of luminaires equipped with electromagnetic or electronic ballasts for fluorescent tube lamps.
There are now tubular LED (“TLED”) lamps which can be used as a direct replacement for traditional fluorescent light tubes. In this way, the advantages of solid state lighting can be obtained without the expense of changing existing light fittings including the existing fluorescent lighting ballast. Indeed, TLEDs that are compatible with fluorescent lamp ballasts are the most straightforward and lowest cost way of replacing fluorescent lighting by LED lighting. Both rewiring (removing the ballast, connecting a TLED directly to AC mains) and replacing the whole luminaire are considerably more cumbersome and expensive. Both electromagnetic (EM) and electronic high frequency (HF) ballasts are used in fluorescent lighting. EM ballast output an AC signal with a frequency at substantially the mains' frequency of 50/60 Hz, and HF ballasts output an AC signal with a frequency of 10 KHz and above. The electronic high frequency ballast further comprises a program start type and a rapid start type with filament heating/detection function, and an instant start type that does not have such functions.
Different tubular LED designs are normally required for connection to EM and HF ballasts.
A problem can arise that a customer does not know what type of ballast is installed within a lighting fixture, so it would be desirable to be able to provide a TLED with compatibility with many different types of ballast.
For completeness, FIG. 1 shows a typical block diagram of a TLED that is compatible with an electronic (high frequency) fluorescent ballast.
The ballast 10 comprises a half-bridge parallel resonant converter and it drives an electronic (high frequency) ballast compatible TLED 12.
The ballast 10 and high frequency compatible TLED 12 are connected via the connection pins 1 and 2 at one end of the TLED and via the connection pins 3 and 4 at the other end of the TLED (shown on one side of the circuit diagram for simplicity).
A high frequency compatible TLED 12 typically comprises some or all of the building blocks depicted in FIG. 1. These are a filament emulation unit 14, a reconfigurable capacitance circuit 16 for standby function, an impedance matching circuit 18, a rectifier 20, an LED driver 22, a smoothing capacitor 23 and the LED string 24.
For most of these building blocks, the implementations shown in FIG. 1 are just examples and other implementations of their functions are possible and are also used. The LED driver shown in FIG. 1 is a shunt switch driver.
The details of the design of the half-bridge ballast 10 are not shown in FIG. 1. This type of ballast is also just an example and other implementations such as push-pull converters are also possible and in use.
The TLED 12 comprises four connection pins that are used to connect it to the ballast 10. Pin 1 and pin 2 are located at one end of the TLED and pin 3 and pin 4 are located at the other end of the TLED. The filament emulation unit comprises first circuitry connecting pin 1 and pin 2 to a pin 5 and pin 3 and pin 4 to a pin 6. Pin safety and start-up circuit 16, matching circuit 18, and rectifier 20 are connected to the ballast only via pin 5 and pin 6.
There are different types of starting technology used within electronic (high frequency) fluorescent ballasts, which give rise to different ballast outputs, and hence different inputs to the connected lamp.
Program and rapid start ballasts rely on a low voltage preheating method so that, when the light switch is turned on, the ballast heats/detects the filament of the lamp then turns on it. Accordingly, the program and rapid start ballasts have a lamp filament heating/detection circuit. The specific heating circuit or detection circuit may be different for a program start ballast and a rapid start ballast, and have different operation durations: less than 500 ms for a rapid start type and more than is for a program start type. Electromagnetic ballasts also have this preheating function similar to the electronic ballasts, and it also comprises a lamp filament heating circuit (whose specific implementation may be different from that of the program start ballast or rapid start ballast). In general, the filament heating/detection circuits in those different types of ballast are called as lamp filament interfacing circuit in this patent application.
Instant start ballasts do not use a preheating method. Instead, they apply a high voltage across the lamp upon initial turning on. Instant start ballasts are used when fluorescent lamps are not switched on and off frequently. Instant start ballasts consume less energy than any other type of lamp ballast.
Program start ballasts are typically paired with occupancy or motion sensors. In this way, the ballast maximizes the number of lamp starting cycles while maintaining energy efficiency. The program start ballast triggers a specific sequence of events to ultimately power on the light. The program for example comprises application of a low voltage across the lamp before supplying voltage to pre-heat the cathodes during a preheat interval. The voltage across the lamp is kept low during the preheat interval to reduce the amount of glow current. A higher voltage is then applied to establish an arc.
These different types of electronic ballast complicate further the compatibility issues.
FIG. 2 shows a typical block diagram of a TLED 30 that is compatible with an EM fluorescent ballast. The TLED 30 comprises a driver 32 which connects to the LED arrangement 34, which is in the form of an LED string.
The LED driver 32 comprises a rectifier, EMI filter, and a driver circuit (e.g., a switch mode power supply circuit, for example a Buck circuit).
The connection pins of the lamp (and the corresponding terminals of the end connectors of the luminaire housing) define a live terminal 1 at one end and a neutral terminal 3 at the other end. EM ballast compatible LED tubes are often designed for single-ended input as shown in FIG. 2, namely a driver being powered by the pins at one end only. A dummy starter 38 (which is typically a fused short) is used to close the current loop between the two ends.
This connection scheme provides protection against pin leakage currents and thus provides pin safety because there is no conductive path from one end of the lamp itself to the other. Therefore, no leakage current can flow if somebody touches the pins at one end while the other end is already energized. The input power is applied to one end of the tube and the other end is provided with a fuse 36 for passing through the current to complete a circuit between external live L and neutral N connections. The glow starter in the fixture is then replaced with the dummy starter 38. The lamp can be installed with either orientation.
However there are also double-ended input LED tubes whose pin safety is an issue generally for connection to electronic ballasts. Various pin safety measures have been proposed. These pin safety measures usually interrupt the electrical connection between both ends of the TLED by at least one switch that is only closed when both ends of the TLED are inserted into the luminaire. However, both electrical and mechanical pin safety mechanisms are known. In mechanical pin safety solutions, at each end of the TLED a switch is closed when pressing a button. Either the lamp holder will push the button when inserting the TLED into the luminaire or it needs to be pressed manually.
There is therefore a need to enable compatibility of a retrofit lamp to different ballast types, and also to ensure pin safety.
U.S. Pat. No. 9,441,795 discloses a retrofit LED lamp which comprises a circuit to detect whether the ballast is an EM ballast or a HF electronic ballast based on frequency or measured current (paragraph [0014]), and to connect LED groups in parallel when connected to a HF ballast (or low current), and in series when connected to an EM ballast (or high current). It is based on adapting the total forward voltage of the LED arrangement to the type of ballast which is present. For a higher voltage EM ballast, more LEDs are in series, therefore with a higher string voltage. The detection of which ballast type is present is for example based on detecting a frequency, output impedance, or rate of change of voltage or current at the output of the ballast.
U.S. Pat. No. 9,144,121 (and US 2013/0127350) discloses a reconfigurable LED array which uses LED pairs which may be connected in series or parallel. The configuration changes the voltage rating of the LED array and its function is to match the mains voltage and providing constant current for different mains voltage. US20170027028A1 also discloses a switching of circuit configuration according to a frequency of the output of the ballast, or a frequency related parameter in current or voltage of the ballast.
A problem with lamps designed for multiple types of ballast is that they have poor energy performance. In particular, in U.S. Pat. No. 9,441,795, the output from different ballasts (current and voltage) differ such that different ballast types will give different efficiency.